This application claims the priority of Germany patent document 198 12 237.3, filed Mar. 20, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and apparatus for regulating the driving dynamics of a road vehicle.
In such method and apparatus reference values are generated by means of a simulation computer of an electronic control unit, under clock control in successive cycles of a predeterminable duration T.sub.K (5 to 10 ms, for example). The control unit implements an automatic regulation process based on a model that represents the vehicle in terms of parameters which depend on its design and its load state as well as its operating data, using measured current values of the vehicle steering angle .delta., vehicle speed v.sub.X and possibly the transverse acceleration a.sub.q for at least the yaw rate .PSI. and the float angle .beta. of the vehicle. Control signals are generated based on a comparison of a setpoint .PSI..sub.SO of the yaw rate of the vehicle with actual values .PSI..sub.I of the yaw rate which are continuously recorded by means of a yaw rate sensor device. The result is used to activate at least one wheel brake of the vehicle and/or reduce the engine driving torque to compensate for deviations in the actual value of each critical setpoint.
A driving dynamics regulating method (FDR) of this kind is known from ATZ Automobiltechnische Zeitschrift, Vol. 96 (1994), No. 11, pages 674 to 689. In this known method, based on the so-called one-track model of a vehicle, a setpoint .PSI..sub.SO is generated according to the relationship ##EQU2##
in which v.sub.CH represents the so-called characteristic speed of the vehicle; a is the distance of the front axle from the center of gravity of the vehicle; and c is the distance of the rear axle from the center of gravity of the vehicle.
The "characteristic speed" v.sub.CH refers to the vehicle-specific speed that corresponds to a maximum of the quotient .PSI./.delta., which is valid for low transverse accelerations .alpha..sub.q.ltoreq.3 ms.sup.-2. Driving dynamics regulation in this case takes the form of state regulation of float angle .beta. and the yaw rate. Float angle .beta., which expresses the difference between the direction of travel and the direction of the lengthwise axis of the vehicle, must not exceed a specified limiting value.
In the driving dynamics regulation explained thus far, because of the manner of generation of the setpoint for the yaw rate of the vehicle, especially when the driver produces a rapid change in the steering angle as the result of an "abrupt" steering maneuver, the actual value of the yaw rate .PSI. of the vehicle deviates drastically from the setpoint. Because of the above-mentioned dependence of the steering angle, such deviation leads the actual value of the yaw rate of the vehicle, which changes more slowly as a result of the inertia of the vehicle, in every case. If the regulation responds in this case, it decreases the lateral guiding force at the rear axle of the vehicle, which in the above situation is undesirable because it causes an oversteering tendency in the wrong direction. At a later point in time such oversteering must be corrected by another regulating intervention. Such a "regulating play", which results from the establishment of an unrealistic setpoint, represents a potential danger that should be avoided.
The goal of the invention therefore is to provide an improved method of the type described above which achieves a setpoint specification for the dynamic state values of the vehicle that corresponds to a realistic movement behavior of the vehicle.
Another object of the invention is to provide a device that is suitable for implementing the method.
These and other objects and advantages are achieved by the control arrangement according to the invention, which generates setpoints for the yaw rate .PSI..sub.S and the float angle .beta..sub.S, corresponding to a dynamically stable behavior of a two-axle vehicle, by means of a clock-controlled evaluation of the following relationships: ##EQU3##
and ##EQU4##
Under the conditions selected according to the invention as stability criteria (namely that the transverse forces produced by rounding a curve as well as the lateral guiding forces that develop as a result of the change in the steering angle .beta.(t) must be compensated, and also that the rotating and yaw moments acting on the vehicle must be compensated) this relationship represents a more realistic model for the dynamic behavior of the real vehicle than the known method for establishing the setpoint of the yaw rate, since the inertial behavior of the vehicle must also be taken adequately into account by the vehicle model used according to the invention.
These relationships can be expressed as a matrix equation in the form EQU [P].multidot.({dot over (X)})=[Q].multidot.(X)+(C).multidot..delta.(t) (I)
in which [P] represents a 4.times.4 matrix with the elements p.sub.ij (p.sub.ij =0,m.sub.Z v,0,0; 0,0,0, J.sub.Z ; 0,0,0,0; 0,-1,0,0), [Q] represents a 4.times.4 matrix with elements q.sub.ij (q.sub.ij =0, -C.sub.V -C.sub.H, 0, -m.sub.Z.multidot.v-(C.sub.V l.sub.V -C.sub.H l.sub.H)/v; 0, C.sub.H l.sub.H -C.sub.V l.sub.V, 0, (-1.sub.v.sup.2 C.sub.v -1.sub.H.sup.2 C.sub.H)/v; 0,0,0,0; 0,0,0,1), C represents a four-component column vector with the components c.sub.i (c.sub.i =C.sub.V,C.sub.V l.sub.V,0,0), X represents a four-component column vector formed of the state values .beta..sub.Z and .PSI..sub.Z with components x.sub.i (x.sub.i =0,.beta..sub.Z,0,.PSI..sub.z) and {dot over (X)} represents the time derivative dX/dt. Evaluation of this relationship takes the form of an updating of the driving dynamic state values .beta..sub.Z (k-1) that have been determined at a point in time t(k-1), to the point in time t(k) that is later by the clock time length T.sub.k, by evaluation of the relationship ##EQU5##
with values of the matrix elements p.sub.ij and q.sub.ij that have been updated to the point t(k) (i.e., determined at that point in time).
The coefficient matrix [P] (associated with the time rates of change, .PSI. and .beta., of the state values .PSI. and .beta. which are to be controlled) of the matrix equation (I) that represents the vehicle reference model, contains only matrix elements that are "absolutely" constant independently of the vehicle data or are vehicle-specifically constant. That is, either they do not change during travel, or they are vehicle-specific constants that are multiplied by the lengthwise speed of the vehicle or are divided by the latter (i.e., values that, with a supportable knowledge of the vehicle-specific values, can be determined at any time from measurements of the lengthwise speed of the vehicle with corresponding accuracy).
The same is also true of the matrix elements of the matrix [Q] associated with the state values .PSI. and .beta. to be regulated, the "state vector," provided they contain terms that are proportional and/or inversely proportional to the lengthwise speed of the vehicle and contain these terms as factors in other vehicle-specific constants.
The diagonal operating stiffness values C.sub.V and C.sub.H in the vehicle reference model describe the vehicle reaction to the setting of a steering angle at a given vehicle speed, with a specific axle and wheel load distribution. These quantities can also be considered as vehicle-specific constants and are determined in adaptive "learning" processes during steady-state rounding of a curve (.PSI.=0,.beta.=0, .delta.=const., v=const.) by evaluating the relationships ##EQU6##
and ##EQU7##
The knowledge of the float angle .beta..sub.Z required for determining the diagonal travel stiffnesses can be obtained (for the case of a vehicle's steady-state rounding of a curve with slight transverse acceleration) by an evaluation of the known relationship .beta..sub.Z =l.sub.H /R.sub.S, wherein R.sub.S represents the road radius of the center of gravity of the vehicle, give by the relationship R.sub.s =(1.sub.H.sup.2 +R.sub.H.sup.2).sup.1/2 ; and R.sub.H represents the average of the road radii of the rear wheels of the vehicle, which can be determined with a knowledge of the wheelbase of the rear wheels from the wheel rpm values of said wheels in accordance with known relationships.
Alternatively or in addition thereto, under the same boundary conditions the float angle .beta..sub.Z, as provided according to Claim 2, can also be determined by an evaluation of the is relationship ##EQU8##
According to another alternative, the float angle .beta..sub.Z can be determined according to the relationship ##EQU9##
in which a.sub.q refers to the vehicle transverse acceleration that builds up with the beginning of the adjustment of a steering angle. This alternative has the advantage that an exact determination of the float angle is possible even with relatively high vehicle transverse accelerations. Hence, a more exact determination of the diagonal travel stiffnesses is also possible, with the transverse acceleration a.sub.q being measured by a transverse acceleration sensor or even determined by computer from the radius of the curve being traveled and the speed of the vehicle.
In a preferred embodiment of the method according to the invention, in order to generate dynamically stable movement behavior of a vehicle, with corresponding setpoints for the state is values of the yaw rate and float angle, a one-track model of a tractor-trailer unit with a one-axle trailer is used to supplement, as it were, the two-axle tractor, with the force and moment equilibrium at the tractor and trailer being selected as a stability criterion once again, according to the relationships
m.sub.z.multidot.v.multidot.(.beta.+.PSI..sub.z)=F.sub.v +F.sub.H -F.sub.G EQU J.sub.2.PSI..sub.z =F.sub.v.multidot.I.sub.v -F.sub.H.multidot.I.sub.H +F.sub.G.multidot.I.sub.G EQU m.sub.A.multidot.v.multidot.(.beta..sub.A +.PSI..sub.A)=F.sub.G +F.sub.A EQU J.sub.A.PSI..sub.A =F.sub.G.multidot.1.sub.AV -F.sub.A.multidot.1.sub.AH
The kinematic coupling (which corresponds to the identity of the speed direction at the articulation point of the tractor and trailer) is taken into account by the relationship ##EQU10##
In this relationship, F.sub.V, F.sub.H, and F.sub.G represent the respective transverse forces acting on the front wheels, rear wheels, and at the articulation point [fifth wheel]; l.sub.G represents the distance of the articulation point from the center of gravity of the tractor; l.sub.Av and l.sub.AH represent the distance of the center of gravity of the trailer from the pivot point and/or the tractor axis; and F.sub.A represents the lateral force acting on the trailer axis. In this vehicle model, the trailer is implemented so to speak only by "additive" values so that it is suitable both for generating setpoints for the tractor alone, and for the tractor-trailer unit as a whole. It can also be modified in suitable fashion and with an explanation, for generating setpoints for a tractor-trailer unit.
In this model of a tractor-trailer unit the float angle .beta..sub.A of the trailer is determined by the relationship ##EQU11##
in which .phi. represents the kink angle formed by the intersection of the lengthwise central planes of the tractor and trailer at the articulation point. This relationship is valid for the case of steady-state travel around a curve in which the tractor and trailer have the same yaw rate .PSI..
The kink angle can be determined by measurement, alternatively or in addition, for the case of steady-state travel around a curve with a relatively low value for the transverse acceleration if the trailer is equipped with wheel rpm sensors.
According to another feature of the invention, by means of an electronic processing unit, relationships that can be evaluated rapidly for the diagonal travel stiffnesses C.sub.V, C.sub.H, and C.sub.A, with which the effective tire lateral forces acting on the wheels are linked by the relationships ##EQU12##
With respect to a device for regulating the driving dynamics in a road vehicle, the goal recited at the outset is achieved by implementing routines in an electronic control unit. This makes it possible to determine adaptively, from measurable parameters on a tractor that is being driven and/or a train consisting of the tractor and a trailer, at least the following values and to store them in a memory so that they can be called up:
a) Total mass m.sub.total of the train, PA0 b) Mass m.sub.Z of the tractor, PA0 c) Mass m.sub.A of the trailer, PA0 d) Wheelbase l.sub.Z of the tractor, PA0 e) Axle load distribution A/P.sub.HA of the tractor, PA0 f) Axle load distribution of the train or the rear axle load P.sub.HA of the trailer as well as routines for estimating the following: PA0 g) Moment of inertia J.sub.Z of the tractor around its main axis, and PA0 h) Moment of inertia J.sub.A of the trailer around its main axis.
During driving, the vehicle operating parameters are constantly compared with reference values, in order to recognize states that are unstable as far as driving dynamics are concerned. By implementing these routines, the vehicle model that serves for generating these reference values is constantly adapted to the current load state of the vehicle, which can be very different from one trip to the next for commercial vehicles. Such adaptive determination of these values also has the advantage that vehicle-specific programming cost for the electronic control unit of the driving dynamics regulating device is minimized. Thus, improper inputs which could result in malfunctions of the regulation during operation of the vehicle cannot occur.
The concept of adaptive determination of practically all data that are significant for effective driving dynamics regulation, makes it possible to set the regulating device for the greatest variety of vehicle types and sizes. It is therefore advantageous, even from the standpoints of economical manufacture and economical use of the regulating device.
In a routine for determining the mass m.sub.Z of a tractor (and possibly the total mass m.sub.total of a tractor-trailer unit or multiple trailer unit, as well as the mass m.sub.A of the trailer) according to another embodiment of the invention, signals that are available from the electronic engine control as well as the output signals from wheel rpm sensors provided for brake and drive-slip regulation, which can also be used to determine the wheelbase l.sub.Z of the tractor, which, alternatively or additionally, can also be determined from the steering angle information, the yaw rate, and the lengthwise speed of the tractor.
A kink angle sensor can be provided in a tractor-trailer unit to determine the angle .phi. at which, when rounding a curve, the vertical lengthwise central planes of the tractor and trailer intersect at the axis of articulation (the fifth wheel), associated with wheel rpm sensors on the wheels of the trailer. In this case, both the length l.sub.A of the trailer and the distance l.sub.SH of the fifth wheel from the rear axle of the tractor can be determined adaptively.
For an adaptive determination of the axle load distribution of a two-axle vehicle (trailer) it is sufficient for the vehicle to be equipped with a single-axle load sensor so that depending on the location of this axle load sensor on the front or rear axle, the distance l.sub.V of its center of gravity from the front axle can be determined in accordance with alternative routines.
Similarly, the mass distribution of the trailer of a tractor-trailer unit (i.e., the distance l.sub.AV of its center of gravity from the fifth wheel) can be determined if the trailer is equipped with an axle load sensor for the load P.sub.AHA supported on the road by the axle of the trailer, and if the tractor is equipped with a rear axle load sensor. Alternatively or in addition, the distance l.sub.AV can be determined adaptively if a load sensor is provided whose output signal is a measure of the mass component m.sub.AS of the trailer supported on the tractor at the fifth wheel.
Estimated values for the yaw moment of inertia J.sub.Z of a tractor (for example a truck with a load state that varies from one trip to the next) and/or for the yaw moment of inertia J.sub.A of a tractor with one or more axles, are sufficiently accurate according to experience for a realistic vehicle model.
In vehicles that have air suspension, an axle load sensing system can be simply implemented by measuring the pressures in the pneumatic wheel springs.
If no axle load sensors are present, it is possible in any case to determine the rear axle load P.sub.HA as well as the front axle load P.sub.VA by braking tests if the tire-specific constants k.sub.HA and k.sub.VA are known. The latter in turn can be determined for the individual wheels.
By means of another routine according to the invention, the current values of the tire constants can be determined continuously. This feature is especially advantageous since these tire constants can be temperature dependent and therefore can change in the course of a trip.
To provide a realistic estimate of the tire constant of a vehicle, it may be sufficient according to another feature of the invention to determine axle-related tire constants k.sub.HA and k.sub.VA for the driven vehicle wheels and the non-driven wheels. In this case, the tire constant is determined for the driven wheels (for example the rear wheels of the vehicle) in the traction mode of the tractor, and the tire constant for the non-driven wheels during braking operation of the vehicle is determined with the value thus known for this tire constant.
In the case of any design of a commercial vehicle with a trailer, either a semitrailer or a towed trailer, it is optimum for both the tractor and the trailer to be equipped with a yaw angle sensor so that a dynamically unstable state of the entire tractor-trailer unit can be recognized quickly and reliably on the basis of different yaw rates of the tractor and the trailer.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.